1.4849 tensile failure

[confused21]

hi Guys

i hope someone can help me out with an issue with material code 1.4849.
our customer has requested we cast test bars and have them tensile tested to meet the required spec:
Tensile :420 MPa
0.2% Yield:220
Elongation: 4%

the results that were received from the test house are:
Tensile :251 MPa
0.2% Yield:217
Elongation: 1%

the test was carried out on on as cast test bar on a keel block

any advice as to achieve the required results would be greatly appreciated.

thanks

 

The casting was undoubtedly faulty in the keel block. I presume the block looked OK visually before testing, so given the very low strength and especially the extremely low elongation, my best guess would be gross porosity.
If the keel block doesn't pass that casting will not. Further investigation is needed here to determine the nature of the defective material

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Metalero]

Hello Posts pics of the fracture surface. Do you have it?

 

[mrfailure]

Easy to check if casting porosity is the problem - look at the tensile fracture surface to see if you can see pores and/or make a longitudinal mount to see porosity in the general structure.

 

[confused21]

further investigation was conducted at the lab on the test piece and sample "displayed an austenitic microstructure typical of 1.4849 steel".
i have tried another keel block sample and the results were not much better.

i have attached a copy of the micro examination.

could these keel blocks have been knocked out sooner or later after casting?

 

The lab should have paused to take a picture in the unetched condition. Do you have that to show us?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Metalero]

Etched micrograph brings some information,(looks like porosity) unetched could be better, but definitely a pic of the tensile fracture surface could be more useful.

 

[Martinos]

36% nickel content means not pores, but shrinkage could be a problem. Is necessary to see fracture surface exactly. Macro and micro.
Micro you showed to us looks OK, but maybe I want to see more uniform interdendritic distribution of M23C6 carbides. You have here 2 types of carbides Cr-rich M23C6 carbides and Nb-rich MC carbides. Quite a lot of precipitates in as-cast gamma matrix in comparison with our production. Porosity level is common, pores are globular.